One exemplary application to which the present invention has utility is that of printing systems. Fluid delivery systems are in common use for delivering liquid ink in printing systems, such as ink-jet printing systems. One type of fluid delivery system is the re-circulating system type. Re-circulating fluid delivery systems are inherently air tolerant. These types of systems move air and ink from the print head region of a print cartridge, separate the air from the ink using either a foam block or by gravity, and circulate the ink back to the print head. The driving force of the re-circulation is generally the same as that to deliver ink.
One type of known re-circulating fluid delivery system employs tubes through which the fluid is delivered. Tubes add significant cost to the fluid delivery system, and increase the amount of force required to drive the print head back and forth during printing. These tube-based systems allow fluid to flow bi-directionally, that is, from the fluid supply to the print head and from the print head to the fluid supply. The system refills the cartridge, with fluid flowing from the supply to the print head. Then, to obtain the correct pressure, excess fluid is caused to flow back from the print head to the fluid supply. The system can overshoot its operating pressure, or set point, and is therefore at risk for overfilling. The set point is negative pressure, referred to as back pressure. If the cartridge were overfilled, poor print quality or drooling out of the nozzles could result.